The present invention relates generally to rim holding tire changers and more particularly to a safety device for use in connection with rim holding tire changers.
It will be appreciated by those skilled in the art of designing and manufacturing equipment used to change the tubeless tires mounted on the rims of cars, trucks and other vehicles that if such equipment is not used correctly and in accordance with instruction, tires can explode and create personal injury and property damage. Manufacturers of such equipment have for years attempted to address this problem with instruction, training manuals, warning decals and hands-on training on their equipment in an attempt to prevent hazards associated with improper use of their equipment. However, not withstanding the efforts made by manufacturers of such equipment to warn and train users, shop mechanics often ignore the training and warnings and use the equipment in a manner contrary to the instructions of the manufacturer. Occasionally, when the rim holding tire changers are used improperly, the results can be catastrophic--an exploded tubeless radial tire that can cause severe personal injury and even death.
The type of equipment for which Applicant's invention is designed is known generally in the industry as a rim holding tire changer and examples of the type of equipment involved are the rim holding tire changers manufactured by Hennessy Industries, Inc., Applicant's assignee, and marketed under the trademarks "COATS.RTM." and "AMMCO.RTM." including the COATS.RTM. models 5030A and the model 5060A-E and 5060AX-EX. However, there are many manufacturers of such equipment, including FMC Corporation of Chicago, Ill., Corghi of Correggio, Italy and Sice of Correggio, Italy. Equipment of this type has been readily available in the market for many years, is the subject matter of numerous patents and has been described in a variety of publications, bulletins, brochures, operating and instruction manuals, and the like. One such machine is illustrated in the design patent issued to Applicant as co-inventor in U.S. Design Pat. No. 293,916.
The misuse of rim holding tire changers occurs in spite of and irrespective of the bold warnings and extensive educational and training efforts of the manufacturers of these products. When accidents occur, lawsuits generally follow and regardless of the efforts of the manufacturers to train users of their equipment in the proper use of rim holding tire changers, the cost of defending such claims can be enormous. In addition, there have been some occasions where damages have been awarded under products liability theories on the basis that the manufacturer of the equipment could have "done more" to protect the user of the equipment against injury.
In order to answer the claim that they should have "done more" to protect the users of their equipment, manufacturers have resorted to a number of safety devices, in addition to the warnings about proper use of their equipment. The safety devices that have been adopted by manufacturers over the years to address the problem of "exploding" tires includes, for example, the enclosure type devices described in U.S. Pat. Nos. 4,840,215; 4,865,104; and 4,811,774, all assigned to FMC Corporation of Chicago, Ill.
The problem with the prior art efforts at "doing something more" in attempting to provide greater safety features in the rim holding tire changing industry is that it is difficult to get the user of the equipment to actually employ the safety devices. In many instances, the mechanic will simply side step the safety measure and proceed with the tire changing process without employing the safety devices built into the equipment.
The particular safety problem involved generally arises during the bead seating step of the tire changing process or in those occasions where there are mismatched tires and wheels. In the automobile industry in the U.S., practically all rim contours conformed to standards established by the Tire and Rim Association, Inc. FIG. 1 illustrates generally a rim contour for a 5.degree. drop center rim for 14", 15", 16", 17" and 18" diameter tire designations and is referred to generally as the J(ISO) contour. Under the rim contour as is illustrated in FIG. 1, there is an annular hump H which serves as a safety feature to keep the inner perimeter of the tire from slipping into the drop center of the rim during certain operations of the vehicle. The hump H, which is employed in the majority of modem rim contours, creates a problem in the mounting of a new tire since the bead of the tire must ride over the hump and the outside diameter of the hump is greater than the inside diameter of the tire. To deal with this problem in the tire mounting process, the bead of the tire must first be sealed against the hump in order to fill the chamber of the tire with compressed air. As compressed air is injected into the chamber, the bead will ride over the hump H and seat against the "j" contour of the perimeter of the rim. After the bead is properly seated, the fire can be inflated to the recommended pressure and the rim is ready to be attached to the hub of the car.
The danger occurs when the bead binds against the hump and does not ride over it to seat against the rim. When this happens, contrary to instructions and warnings, mechanics tend to continue to force compressed air into the tire chamber far beyond the recommended pressure of approximately 40 psi for a standard automobile fire. As the pressure within the chamber builds up, the mechanic often will peer over the tire to see if the bead has seated against the rim. When the bead actually does ride over the hump, the pressure within the chamber of the tire will cause the bead to accelerate at a tremendous rate and be impelled against the rim. The force of the bead against the rim can cause the tire and/or the rim to explode and if the mechanic is peering over the tire, the explosion occurs in his face and can cause tremendous injury or death.
The other occasion which can create the type of problem discussed above is when a mechanic attempts to mount a mis-matched tire/rim combination.
Automobile tires are generally mounted on even sized wheels of 14", 15", 16", 17", etc. The automobile industry for a number of years used half-sized rims on small trucks such as pick-up trucks. Thus, the trucks would have rim diameters of 16.5", 17.5", etc. In the early 1980's, 16" tires on pick-up trucks became popular and the 16.5" tires lost favor because of extra expense, etc. However, in the older pick-up trucks, the customer would have a 16.5" rim and when he took his pick-up truck by a tire dealer to have a new set of fires mounted on his truck, occasionally a mechanic would pull a 16" tire from inventory and attempt to mount a 16" tire on a 16.5" rim (the 16" tire on a 16.5" rim is the predominant problem of mismatched tires although the problem could occur in other sized rim/tire combinations such as the attempt to mount a 17" tire on a 17.5" rim, etc.). Mounting an even sized tire on a half-sized wheel simply is not possible. The bead of a 16" tire will not seat properly on a 16.5" rim or wheel, and continuing to apply compressed air into the chamber of a tire will eventually result in an explosion of the tire or the tire and the wheel. If the mechanic is peering over the tire to see if the bead is properly seated, he will in all likelihood be severely injured.
In a number of rim holding tire changers currently on the market, foot pedals are used to apply air pressure within the chamber of a tire that is being mounted on a rim. When the bead is being sealed against the hump, the first foot pedal or the initial depression of a foot pedal will cause compressed air to flow through the valve in the rim. Modem rim holding tire changers also include table top jets which blast air at approximately 140 psi from the table top to create an air curtain which aids in the bead sealing. At this stage in the process, approximately 10 psi air pressure within the tire chamber is the maximum recommended pressure. Generally, the tire will contain about 1/2 to 2 psi of air pressure when the bead seal is obtained.
Once bead sealing is achieved, the second foot pedal is depressed or a single foot pedal is depressed to a second stage so that air is injected into the tire chamber. Since the bead is now sealed against the hump, there is no need for air pressure through the table top jets so at the second step of process, the only air pressure to the tire is the air to seat the bead against the rim through the valve in the rim. Bead seating will usually require at least 7 psi in the tire, but 40 psi is the maximum safe pressure at this stage regardless of tire operating pressure.
At the bead seating stage of the process, since the foot pedal for introducing pressure into the chamber of the tire is directly at the base of the tire changer, it is possible for the mechanic to peer over the top of the tire while he depresses the foot pedal and forces additional air pressure within the chamber which, if the tire explodes while he is looking at the bead, could result in personal injury.